In conventional scroll compressors of this type, opposed surfaces of a fixed scroll and a end plate of an orbiting scroll are provided with an annular seal portion and an annular recess located outside of this seal portion (see patent document 1 for example).
FIG. 6 shows the conventional scroll compressor described in the patent document 1. As shown in FIG. 6, a fixed scroll 202 has a scroll lap 221b, and an orbiting scroll (not shown) existing on an outer side of the scroll lap 221b has a end plate. An annular seal portion 213 and an annular recess 214 are formed in a surface of the fixed scroll 202 opposed to the end plate. The seal portion 213 extends such as to have an outer wall surface 221c which extends from inner wall surfaces 215a to 215d of outermost periphery of the scroll lap 221b substantially along the inner wall surfaces 215a to 215d, and comes into slide contact with the end plate of the orbiting scroll. The annular recess 214 is located on the outer side of the seal portion 213.
(Patent Document 1)
Japanese Patent Application Laid-open No. 2001-355584
According to the conventional structure, however, even if back pressure is applied to the orbiting scroll, the same back pressure acts on the annular recess 214 and as a result, the back pressure is reduced. Therefore, even if predetermined back pressure force is applied, the back pressure force of the orbiting scroll is prone to be reduced depending upon operating condition of the scroll compressor. With high efficiency tendency of recent freezer air conditioners, scroll compressors are extremely frequently operated with low compression ratio, and there is a problem that the orbiting scroll is separated from the fixed scroll 202 under such operating condition, and the scroll compressor is operated while the orbiting scroll is turned over. Further, in a scroll compressor used for a heat pump type water heating system, the scroll compressor is operated with much lower compression ratio than that of the freezer air conditioner depending upon a water heating condition, and the orbiting scroll is separated from the fixed scroll 202 more frequently.
The present invention has been achieved to solve such conventional problems, and it is an object of the invention to provide a efficient and reliably scroll compressor capable of reducing sliding lost at a thrust portion while suppressing the turning-over phenomenon of the orbiting scroll when the compressor is operated with low compression ratio.